Although existing treatments benefit many families of children with disruptive behavior problems, a substantial proportion do not respond to treatment. A better understanding of treatment mechanisms will illuminate reasons for nonresponse and point to strategies for improving treatment. To achieve this goal, systematic research on specific treatment targets (not just symptom reduction) is needed. This application focuses on skill acquisition and utilization as specific treatment targets or hypothesized mechanisms of therapeutic action for cognitive behavioral therapy (CBT) for childhood disruptive behavior problems. Specifically, this project consists of a small pilot RCT to examine target engagement and validation (acquisition and utilization of specific CBT skills) of a smartphone based mobile health (mHealth) system called UseIt! (Understanding Skill- use to Enhance the Impact of Treatment). The project will also establish the feasibility of this novel research protocol and refine the smartphone applications (apps) and secure online clinician portal. The parent and child UseIt! apps include both content and features to promote the use of CBT skills in day-to-day life including a library of skills, an interactive trouble-shooting guide, an electronic diary,a secure messaging system, and a skill-use reminder alarm. The project will also establish the feasibility of incorporating recently developed measures of skill acquisition (Skill Acquisition Measure [SAM]) and skill utilization (Skill-use Internet Diary [SID]) into a treatment trial. Childen with significant disruptive behavior problems (ages 8-12) and their parents will be recruited directly from partnering community agencies. Aim 1 of the project is to assess target engagement and validation in the context of a preliminary RCT comparing CBT + UseIt! protocol (N=18) to CBT only (N=18). Aim 2 is to assess the feasibility of a future full-scale effectiveness RCT comparing these treatments, and incorporating measures of skill acquisition and skill utilization into a treatment trial. Aim 3 is to refine the UseIt! apps and clinician portal, and to integrate the technology seamlessly with treatment delivery, based on feedback obtained from clinicians and families. This approach is consistent with treatment development pathways recommended in the R34 mechanism and also responsive to strategies outlined in the NIMH Strategic Plan for improving personalization of treatments by providing customized in vivo skills coaching, and for improving potential dissemination of child psychosocial treatments by making them more efficient, interactive, and engaging. This will provide the preliminary data necessary to prepare for a full-scale effectiveness RCT (R01).